Magnetic resonance imaging method and device for lumbar vertebra, computer equipment, readable storage medium and program product

Abstract

The invention relates to a magnetic resonance imaging method and device for lumbar vertebrae, computer equipment, a computer readable storage medium and a computer program product, relates to the technical field of magnetic resonance, and can improve the accuracy of water-fat separation of a high-resolution lumbar vertebrae imaging image. The method comprises the following steps: acquiring an echo sequence aiming at the lumbar vertebra in a magnetic resonance imaging process; the echo sequence comprises water-fat in-phase echo signals corresponding to different echo times; according to the signal intensity of each water-fat in-phase echo signal, the echo time of each water-fat in-phase echo signal and a pre-constructed signal model, determining an initial transverse relaxation rate graph corresponding to the lumbar vertebra and an initial field graph representing the non-uniformity of a static magnetic field applied to the lumbar vertebra; and taking the initial transverse relaxation rate graph and the initial field graph as initial reconstruction parameters of water-fat separation, and reconstructing a water-fat separation image of the lumbar vertebra.

Description

Technical Field

[0001] The present application relates to the field of magnetic resonance technology, and particularly to a magnetic resonance imaging method, device, computer device, computer-readable storage medium, and computer program product for the lumbar spine. Background Art

[0002] With the rapid development of magnetic resonance imaging technology, multi-parameter quantitative imaging technology has received extensive attention because it can obtain multiple quantitative imaging parameters and provide rich information for clinical analysis. The main source of magnetic resonance imaging signals is hydrogen protons in water (i.e., H protons). Since the fat content in the lumbar spine is high, the signals generated by fat hydrogen protons during magnetic resonance imaging cannot be ignored, and the corresponding signal model is more complex than a single water hydrogen proton imaging model. Water-fat separation is required to achieve multi-parameter quantitative imaging.

[0003] In related technologies, water-fat separation imaging is mainly based on low-resolution images. For high-resolution lumbar spine imaging images, the water-fat separation process is easily interfered by image noise, and it is difficult to achieve accurate water-fat separation. Summary of the Invention

[0004] Based on this, in order to solve the above technical problems, it is necessary to provide a magnetic resonance imaging method, device, computer device, computer-readable storage medium, and computer program product for the lumbar spine.

[0005] In a first aspect, the present application provides a magnetic resonance imaging method for the lumbar spine, including:

[0006] Obtaining an echo sequence for the lumbar spine during magnetic resonance imaging; the echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signals are signals collected when the hydrogen protons in water and fat are in the same phase;

[0007] According to the signal intensities of the water-fat in-phase echo signals, the echo times of the water-fat in-phase echo signals, and a pre-constructed signal model, determining an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the inhomogeneity of the static magnetic field applied to the lumbar spine; the signal intensity of the water-fat in-phase echo signal in the signal model is a signal jointly determined by the transverse relaxation rate map at the moment when the hydrogen protons in water and fat are in the same phase and the inhomogeneous magnetic field map of the static magnetic field;

[0008] Using the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation, and reconstructing the water-fat separation image of the lumbar spine.

[0009] In one embodiment, the water-fat in-phase echo signals include multiple water-fat in-phase echo signals obtained by exciting with multiple radio frequency pulses, and the multiple water-fat in-phase echo signals correspond to different flip angles;

[0010] The method further includes:

[0011] Obtain a proton density map and a longitudinal relaxation time map of the lumbar spine according to the initial transverse relaxation rate map, the flip angles corresponding to the multiple water-fat in-phase echo signals respectively, and the repetition time between the multiple radio frequency pulse excitations.

[0012] In one embodiment, the water-fat in-phase echo signals correspond to water-fat in-phase echo images with a first resolution;

[0013] The flip angle corresponding to the water-fat in-phase echo signal is determined by the following steps:

[0014] Obtain an initial radio frequency field map corresponding to the radio frequency pulse excitation; the second resolution corresponding to the initial radio frequency field map is less than the first resolution;

[0015] Adjust the initial radio frequency field map with the second resolution to the first resolution to obtain a target radio frequency field map;

[0016] Determine the flip angle of the radio frequency pulse excitation according to the target radio frequency field map as the flip angle corresponding to the water-fat in-phase echo signal.

[0017] In one embodiment, adjusting the initial radio frequency field map with the second resolution to the first resolution includes:

[0018] Perform linear interpolation on the initial radio frequency field map with the second resolution to obtain the initial radio frequency field map with the first resolution.

[0019] In one embodiment, the echo sequence further includes multiple water-fat out-of-phase echo signals, and the water-fat out-of-phase echo signals are signals collected when the hydrogen protons of water and fat in the lumbar spine are in different phases;

[0020] Reconstructing the water-fat separation image of the lumbar spine by using the initial transverse relaxation rate map and the initial field map as the initialization reconstruction parameters for water-fat separation includes:

[0021] Use the initial transverse relaxation rate map and the initial field map as the initialization reconstruction parameters for water-fat separation;

[0022] Perform water-fat separation image reconstruction according to the initialization reconstruction parameters, the water-fat out-of-phase echo signals, and the water-fat in-phase echo signals;

[0023] Obtain the water image and fat image of the lumbar spine according to the reconstruction result, and determine the tissue fraction map of the lumbar spine according to the water image and fat image of the lumbar spine.

[0024] In one embodiment, after the step of performing water-fat separation image reconstruction according to the initialized reconstruction parameters, the water-fat opposed-phase echo signal, and the water-fat in-phase echo signal, the method further includes:

[0025] Obtain a target field map according to the reconstruction result; the target field map is obtained by iteratively updating the initial field map during the water-fat separation image reconstruction process;

[0026] Obtain the quantitative susceptibility map corresponding to the lumbar spine according to the target field map.

[0027] In a second aspect, the present application further provides a magnetic resonance imaging device for the lumbar spine, including:

[0028] A sequence acquisition module, configured to acquire an echo sequence for the lumbar spine during a magnetic resonance imaging process; the echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signals are signals acquired when the hydrogen protons of water and fat are in the same phase;

[0029] An initial parameter estimation module, configured to determine an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the inhomogeneity of the static magnetic field applied to the lumbar spine according to the signal intensity of each water-fat in-phase echo signal, the echo time of each water-fat in-phase echo signal, and a pre-constructed signal model; the signal intensity of the water-fat in-phase echo signal in the signal model is a signal jointly determined by the transverse relaxation rate map at the moment when the hydrogen protons of water and fat are in the same phase and the inhomogeneous field map of the static magnetic field;

[0030] A water-fat separation module, configured to use the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation, and reconstruct the water-fat separation image of the lumbar spine.

[0031] In a third aspect, the present application further provides a computer device, including a memory and a processor, where the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0032] Acquire an echo sequence for the lumbar spine during a magnetic resonance imaging process; the echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signals are signals acquired when the hydrogen protons of water and fat are in the same phase;

[0033] Determine an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the static magnetic field inhomogeneity applied to the lumbar spine according to the signal intensities of the respective water-fat in-phase echo signals, the echo times of the respective water-fat in-phase echo signals, and a pre-constructed signal model; in the signal model, the signal intensity of the water-fat in-phase echo signal is a signal jointly determined by the transverse relaxation rate map at the in-phase moment of the hydrogen protons of water and fat and the static magnetic field inhomogeneity field map.

[0034] Use the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation to reconstruct the water-fat separation image of the lumbar spine.

[0035] In a fourth aspect, the present application further provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the following steps are implemented:

[0036] Obtain an echo sequence for the lumbar spine during magnetic resonance imaging; the echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signals are signals collected when the hydrogen protons of water and fat are in the same phase.

[0037] Determine an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the static magnetic field inhomogeneity applied to the lumbar spine according to the signal intensities of the respective water-fat in-phase echo signals, the echo times of the respective water-fat in-phase echo signals, and a pre-constructed signal model; in the signal model, the signal intensity of the water-fat in-phase echo signal is a signal jointly determined by the transverse relaxation rate map at the in-phase moment of the hydrogen protons of water and fat and the static magnetic field inhomogeneity field map.

[0038] Use the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation to reconstruct the water-fat separation image of the lumbar spine.

[0039] In a fifth aspect, the present application further provides a computer program product, including a computer program, and when the computer program is executed by a processor, the following steps are implemented:

[0040] Obtain an echo sequence for the lumbar spine during magnetic resonance imaging; the echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signals are signals collected when the hydrogen protons of water and fat are in the same phase.

[0041] According to the signal intensities of the respective water-fat in-phase echo signals, the echo times of the respective water-fat in-phase echo signals, and a pre-constructed signal model, an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the static magnetic field inhomogeneity applied to the lumbar spine are determined; in the signal model, the signal intensity of the water-fat in-phase echo signal is a signal jointly determined by the transverse relaxation rate map at the in-phase moment of the hydrogen protons of water and fat and the static magnetic field inhomogeneity field map.

[0042] Using the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation, a water-fat separation image of the lumbar spine is reconstructed.

[0043] The above-mentioned magnetic resonance imaging method, device, computer device, computer-readable storage medium, and computer program product for the lumbar spine can obtain an echo sequence for the lumbar spine during magnetic resonance imaging. The echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signal is a signal collected when the hydrogen protons of water and fat are in the same phase. Then, according to the signal intensities of the respective water-fat in-phase echo signals, the echo times of the respective water-fat in-phase echo signals, and a pre-constructed signal model, an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the static magnetic field inhomogeneity applied to the lumbar spine are determined. In the signal model, the signal intensity of the water-fat in-phase echo signal is a signal jointly determined by the transverse relaxation rate map at the in-phase moment of the hydrogen protons of water and fat and the static magnetic field inhomogeneity field map. Furthermore, the initial transverse relaxation rate map and the initial field map can be used as initialization reconstruction parameters for water-fat separation to reconstruct a water-fat separation image of the lumbar spine. In this embodiment, by obtaining the water-fat in-phase echo signal of the lumbar spine, when the fat content in the lumbar spine is relatively high, the signals generated by the hydrogen protons of water and fat can be regarded as combined signals generated by the same type of hydrogen protons, effectively simplifying the magnetic resonance imaging signal model for the lumbar spine. Then, based on the simplified signal model, accurate initial estimation results can be obtained for the field map and the transverse relaxation rate map, effectively improving the accuracy of subsequent water-fat separation of high-resolution lumbar spine images. At the same time, it also creates sufficient technical conditions for realizing multi-parameter quantitative imaging of the lumbar spine. Description of the Drawings

[0044] To more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments of the present application or related technologies. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0045] Figure 1 It is a schematic flowchart of a magnetic resonance imaging method for the lumbar spine in an embodiment.

[0046] Figure 2 It is a schematic flowchart of the steps for determining the flip angle in an embodiment;

[0047] Figure 3 It is a schematic flowchart of another magnetic resonance imaging method for the lumbar spine in an embodiment;

[0048] Figure 4 It is a circuit diagram of a high - resolution multi - parameter quantitative imaging technology for the lumbar spine in an embodiment;

[0049] Figure 5 It is a structural block diagram of a magnetic resonance imaging device for the lumbar spine in an embodiment;

[0050] Figure 6 It is an internal structure diagram of a computer device in an embodiment;

[0051] Figure 7 It is an internal structure diagram of another computer device in an embodiment. Specific implementation manners

[0052] In order to make the objectives, technical solutions and advantages of this application more clear and understandable, the following further elaborates on this application in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0053] In order to enable those skilled in the art to better understand this application, the related technologies will be introduced first below.

[0054] With the rapid development of magnetic resonance imaging technology, multi - parameter quantitative imaging technology has received extensive attention because it can obtain multiple quantitative imaging parameters and provide rich information for clinical analysis. Among them, the multi - parameter quantitative imaging models used are complex, and there are differences between the signal models of different imaging sequences or imaging parts. Therefore, for different imaging sequences and imaging parts, targeted algorithms need to be designed to obtain accurate and reliable quantitative imaging parameters.

[0055] The main source of magnetic resonance imaging signals is hydrogen protons in water (i.e., H protons). In related technologies, the fat content in some tissue structures is very low, and the signals generated by hydrogen protons in fat can be ignored, thus effectively simplifying the imaging signal model. For example, in magnetic resonance multi - parameter quantitative imaging technology for the brain, the signals generated by hydrogen protons in fat can be ignored, greatly simplifying the signal model. However, the fat content in the lumbar spine is high, and the signals generated by hydrogen protons in fat during magnetic resonance imaging cannot be ignored. Moreover, the precession frequencies of hydrogen protons in fat and water are different, and its signal model is more complex than the single - water - hydrogen - proton imaging model in the head. To achieve multi - parameter quantitative imaging, water - fat separation is required.

[0056] In related technologies, water-fat separation imaging is mainly based on low-resolution images. Since the signal-to-noise ratio of low-resolution images is high, water-fat separation can often be achieved more accurately. However, in high-resolution lumbar imaging, the signal-to-noise ratio of the image decreases, and the water-fat separation process is easily interfered by image noise, making it difficult to achieve precise water-fat separation.

[0057] Based on this, it is necessary to provide a magnetic resonance imaging method, device, computer device, computer-readable storage medium, and computer program product for the lumbar spine to address the above technical problems.

[0058] In one embodiment, as Figure 1 shown, a magnetic resonance imaging method for the lumbar spine is provided. In this embodiment, the method is exemplified by being applied to a terminal. It can be understood that the method can also be applied to a server, and can also be applied to a system including a terminal and a server, and is implemented through the interaction between the terminal and the server. In this embodiment, the method includes the following steps:

[0059] S101, obtaining an echo sequence for the lumbar spine during magnetic resonance imaging; the echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signals are signals collected when the hydrogen protons of water and fat are in the same phase.

[0060] Specifically, magnetic resonance imaging utilizes the characteristics of hydrogen protons in the magnetic field of tissue structures. In a static magnetic field environment, the magnetic moments of hydrogen protons will align along the magnetic field direction and be in a low-energy state. When a radiofrequency pulse is applied, the energy of the radiofrequency pulse is absorbed by the hydrogen protons, causing the magnetic moments of the hydrogen protons to deflect and generating a transverse magnetization vector. At this time, the hydrogen protons are in an excited state. After the radiofrequency pulse stops, the hydrogen protons begin to recover from the excited state to the equilibrium state, and this process is called relaxation. During the relaxation process, the transverse magnetization vector will precess around the main magnetic field direction, and due to the interaction between protons and the slight differences in the magnetic field environment they are in, the transverse magnetization vector will gradually decay. This decaying transverse magnetization vector will generate an induced current in the receiving coil, thereby generating an electromagnetic signal that can be detected, that is, an echo. By arranging a series of radiofrequency pulses and / or gradient field pulse combinations in a specified time sequence and parameter settings, an echo sequence containing multiple echoes can be obtained.

[0061] Water and fat in the tissue structure are two main sources of hydrogen protons. The hydrogen protons in water and fat have different precession frequencies in magnetic resonance imaging. Under a specified magnetic field environment and radiofrequency pulse sequence, due to the different chemical shifts of hydrogen protons in water and fat, the signal phases of hydrogen protons in water and fat will change over time. When the hydrogen protons in water and fat are in the same phase, the echo signal collected at this time is the in-phase water-fat echo signal. For example, in a gradient echo sequence, by adjusting parameters such as the flip angle of the radiofrequency pulse, the intensity and duration of the gradient field, the signals of water and fat can be in the same phase at a specific moment, and then the in-phase water-fat echo signal can be obtained.

[0062] In this step, an echo sequence collected for the lumbar spine during magnetic resonance imaging can be obtained. The collected echo sequence may include multiple in-phase water-fat echo signals, and the multiple in-phase water-fat echo signals correspond to different echo times. In some examples, the echo sequence can be a gradient echo sequence.

[0063] S102. According to the signal intensity of each in-phase water-fat echo signal, the echo time of each in-phase water-fat echo signal, and a pre-constructed signal model, determine the initial transverse relaxation rate map corresponding to the lumbar spine and the initial field map characterizing the inhomogeneity of the static magnetic field applied to the lumbar spine; the signal intensity of the in-phase water-fat echo signal in the signal model is the signal jointly determined by the transverse relaxation rate map and the static magnetic field inhomogeneity field map at the moment when the hydrogen protons in water and fat are in the same phase.

[0064] In practical applications, a corresponding signal model can be pre-constructed based on the in-phase water-fat echo signal. Specifically, at the acquisition moment of the in-phase water-fat echo signal, the signals generated by hydrogen protons in water and hydrogen protons in fat have the same signal phase. Based on this, the signal model can be simplified, and the signals generated by hydrogen protons in water and hydrogen protons in fat can be merged and regarded as a combined signal generated by the same type of hydrogen protons. Then, the correlation relationship between the signal intensity of the in-phase water-fat echo signal, the echo time, the transverse relaxation rate map, the field map of the static magnetic field, and the combined signal can be constructed to obtain the signal model. In this signal model, the signal intensity of the in-phase water-fat echo signal can be jointly determined by the transverse relaxation rate map and the field map of the static magnetic field inhomogeneity at the moment when the hydrogen protons in water and fat are in the same phase. In one example, the signal model can be as follows:

[0065]

[0066] Among them, is the signal intensity of the th in-phase water-fat echo signal, is the signal generated by hydrogen protons in water, is the signal generated by hydrogen protons in fat, is the combined signal generated by hydrogen protons in water and hydrogen protons in fat, is the echo time of the nth water-fat in-phase echo signal, is the transverse relaxation rate map,

[0067] Furthermore, after obtaining the echo sequence, the transverse relaxation rate map for the lumbar spine and the field map characterizing the inhomogeneity of the externally applied magnetic field can be calculated based on the signal intensity of the water-fat in-phase echo signal in the echo sequence, the echo time of each water-fat in-phase echo signal determined during the magnetic resonance imaging process, and the pre-constructed signal model. For ease of distinction, in this step, the transverse relaxation rate map and the field map determined based on the above signal model are respectively referred to as the initial transverse relaxation rate map and the initial field map.

[0068] S103, using the initial transverse relaxation rate map and the initial field map as the initialization reconstruction parameters for water-fat separation, reconstruct the water-fat separation image of the lumbar spine.

[0069] Specifically, in magnetic resonance imaging, water-fat separation refers to using the different characteristics of hydrogen protons in water and fat to separately display the signals of water and fat and obtain a water image and a fat image.

[0070] In this step, after estimating the initial transverse relaxation rate map and the initial field map, the initial transverse relaxation rate map and the initial field map can be used as the initialization reconstruction parameters for water-fat separation, where the initialization reconstruction parameters refer to the parameters used as initialization information during the iterative reconstruction process of the water-fat separation image. Then, the initial transverse relaxation rate map and the initial field map can be substituted into the relevant water-fat separation reconstruction algorithm, and based on the iterative results of the algorithm, the water-fat separation image of the lumbar spine, that is, the water image and the fat image of the lumbar spine, can be reconstructed.

[0071] In some exemplary embodiments, water-fat separation image reconstruction can be performed based on any one of dual echo opposed-phase imaging, multi-echo Dixon technique, iterative decomposition water-fat imaging, etc.

[0072] Among them, the multi-echo Dixon technique can collect echo signals with multiple different echo times, utilize the phase change law of water and fat signals at different echo times, and process the multiple echo signals through complex mathematical algorithms to accurately separate the water and fat signals.

[0073] Iterative decomposition water-fat imaging is model-driven. By establishing a water-fat signal model and using an iterative algorithm to decompose the collected magnetic resonance signals, water-fat separation can be achieved.

[0074] In the above magnetic resonance imaging method for the lumbar spine, an echo sequence for the lumbar spine during the magnetic resonance imaging process can be obtained. The echo sequence includes water-fat in-phase echo signals corresponding to different echo times. The water-fat in-phase echo signals are signals acquired when the hydrogen protons of water and fat are in the same phase. Then, based on the signal intensities of the water-fat in-phase echo signals, the echo times of the water-fat in-phase echo signals, and a pre-constructed signal model, an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the inhomogeneity of the static magnetic field applied to the lumbar spine can be determined. The signal intensity of the water-fat in-phase echo signal in this signal model is a signal jointly determined by the transverse relaxation rate map at the moment when the hydrogen protons of water and fat are in the same phase and the inhomogeneous magnetic field map of the static magnetic field. Furthermore, the initial transverse relaxation rate map and the initial field map can be used as initialization reconstruction parameters for water-fat separation to reconstruct the water-fat separation image of the lumbar spine. In this embodiment, by acquiring the water-fat in-phase echo signals of the lumbar spine, when the fat content in the lumbar spine is relatively high, the signals generated by the hydrogen protons of water and fat can be regarded as combined signals generated by the same type of hydrogen protons, effectively simplifying the magnetic resonance imaging signal model for the lumbar spine. Then, based on the simplified signal model, accurate initial estimation results (i.e., the initial transverse relaxation rate map and the initial field map) can be obtained for the field map and the transverse relaxation rate map, effectively improving the accuracy of subsequent water-fat separation of high-resolution lumbar spine images. At the same time, it also creates sufficient technical conditions for realizing multi-parameter quantitative imaging of the lumbar spine.

[0075] In an exemplary embodiment, the water-fat in-phase echo signals include multiple water-fat in-phase echo signals obtained by multiple radiofrequency pulse excitations, and the multiple water-fat in-phase echo signals correspond to different flip angles. Among them, the flip angle, also known as the tipping angle, refers to the angle at which the magnetization vector of hydrogen protons flips from the initial longitudinal direction (consistent with the direction of the main magnetic field) to the transverse plane when a radiofrequency pulse acts on the hydrogen protons in the tissue structure during magnetic resonance imaging. In some embodiments, two or more flip angles can be used to obtain multiple water-fat in-phase echo signals. Exemplarily, when the signal-to-noise ratio in the water-fat in-phase echo is relatively high (for example, higher than a preset signal-to-noise ratio threshold), a smaller flip angle (for example, an angle less than a preset angle threshold) can be adopted. For example, two flip angles α1 and α2 are 3 degrees and 15 degrees respectively.

[0076] Correspondingly, the method may further include the following steps:

[0077] Based on the initial transverse relaxation rate map, the flip angle corresponding to each of the multiple water-fat in-phase echo signals, and the repetition time between multiple radiofrequency pulse excitations, obtain the proton density map and the longitudinal relaxation time map of the lumbar spine.

[0078] Specifically, the repetition time (TR) between multiple radiofrequency pulse excitations can be determined. The repetition time refers to the time interval between two adjacent radiofrequency pulse excitations, which can determine the cycle of magnetic resonance signal acquisition. After each radiofrequency pulse excitation, the hydrogen protons in the tissue will undergo a relaxation process. TR is to give the hydrogen protons enough time to relax so that a detectable magnetic resonance signal can be generated during the next excitation. For example, in a pulse sequence, if the repetition time is set to 1000 ms, then a radiofrequency pulse will be applied for signal excitation every 1000 ms.

[0079] In this embodiment, after obtaining multiple in-phase water-fat echo signals and determining the flip angles of each in-phase water-fat echo signal, the proton density map (PD) and the T1 relaxation map of the lumbar spine can be obtained based on the initial transverse relaxation rate map estimated in step S102, the multiple in-phase water-fat echo signals, the flip angles corresponding to the multiple in-phase water-fat echo signals, and the repetition time between multiple radiofrequency pulse excitations.

[0080] In some exemplary embodiments, since the transverse relaxation rate map can reflect the transverse relaxation characteristics of the tissue, when obtaining the proton density map, the signal can be corrected by combining the transverse relaxation rate map. For example, for tissues with fast transverse relaxation, their signals decay quickly. If the proton density is judged only based on the echo signal intensity, errors will occur. The transverse relaxation rate map can compensate for this signal decay, so as to more accurately reflect the proton density. After processing the in-phase water-fat echo signals at different flip angles and removing the influence of relaxation and other factors, the signal intensity distribution obtained can reflect the proton density distribution, and then a proton density map is generated.

[0081] On the other hand, after applying radiofrequency pulses with different flip angles, the longitudinal magnetization vector of the tissue will be flipped and restored to different extents. Among the in-phase water-fat echo signals with multiple different flip angles, the collected signals contain information about the recovery process of the longitudinal magnetization vector. By analyzing the change of signal intensity with time at different flip angles, the recovery curve of the longitudinal magnetization vector can be obtained.

[0082] For example, according to the basic theory of magnetic resonance signal intensity, there is a mathematical relationship between the signal intensity S and parameters such as proton density PD, longitudinal relaxation time T1, flip angle α, repetition time TR, etc., which can be expressed as S = PD × f(α, TR, T1), where f(α, TR, T1) is a function related to the flip angle, repetition time, and longitudinal relaxation time. Select the signal intensities S1 and S2 at two different flip angles α1 and α2. According to the formula, we can get S1 = PD × f(α1, TR, T1) and S2 = PD × f(α2, TR, T1). By solving these two equations simultaneously to eliminate the influence of PD, the expression of T1 can be obtained, and then by calculating each pixel point, the longitudinal relaxation time map can be obtained. In actual calculation, a more complex multi-flip angle data fitting method can also be used to improve the calculation accuracy and stability.

[0083] In some exemplary embodiments, the PD map and T1 quantitative image can be calculated according to the following formula.

[0084]

[0085]

[0086]

[0087] Where, is the water-fat in-phase echo signal corresponding to the i-th flip angle; is the flip angle size; is the initial transverse relaxation rate map; is the repetition time; is the longitudinal relaxation time.

[0088] In this embodiment, after obtaining the initial transverse relaxation rate map determined according to the water-fat in-phase echo, the proton density map and the longitudinal relaxation time map can be quantitatively calculated by further combining the accurate and reliable initial transverse relaxation rate map, which helps to obtain reliable multi-parameter quantitative imaging results for the lumbar spine.

[0089] In an exemplary embodiment, the water-fat in-phase echo signal can be presented by a water-fat in-phase echo image. For example, according to the water-fat in-phase echo signal, a water-fat in-phase echo image can be reconstructed. For the convenience of distinction, the resolution corresponding to the water-fat in-phase echo image is called the first resolution. As Figure 2 shown, the flip angle corresponding to the water-fat in-phase echo signal can be determined by the following steps:

[0090] S201, obtain the initial radiofrequency field map corresponding to the radiofrequency pulse excitation; the second resolution corresponding to the initial radiofrequency field map is less than the first resolution.

[0091] In a specific implementation, when determining the proton density map and longitudinal relaxation time map of the lumbar spine based on the water-fat in-phase echo signals at multiple flip angles, the accuracy of the flip angle has a great influence on the parameter quantification result. For example, it is intended to use radiofrequency to flip the magnetization vector of hydrogen protons by 3 degrees, but the actual flip angle may be only 2.9 degrees. If the subsequent calculations are directly based on the flip angle of 3 degrees, the accuracy of the proton density map and longitudinal relaxation time map will be affected.

[0092] For this reason, in this embodiment, the radiofrequency field map B1 corresponding to the radiofrequency pulse excitation can be obtained. For the convenience of distinction, the radiofrequency field map B1 without resolution adjustment is referred to as the initial radiofrequency field map, and at the same time, the resolution corresponding to the initial radiofrequency field map is referred to as the second resolution. In a specific implementation, the initial radiofrequency field map can be obtained by rapid sweep, and the second resolution of the initial radiofrequency field map is less than the first resolution.

[0093] S202, adjust the initial radiofrequency field map with the second resolution to the first resolution to obtain the target radiofrequency field map.

[0094] After obtaining the initial radiofrequency field map with the second resolution, its resolution can be adjusted, that is, the initial radiofrequency field map with the second resolution is adjusted to the first resolution, and then the radiofrequency field map after resolution adjustment can be referred to as the target radiofrequency field map.

[0095] S203, determine the flip angle of the radiofrequency pulse excitation according to the target radiofrequency field map as the flip angle corresponding to the water-fat in-phase echo signal.

[0096] Since the radiofrequency field map B1 contains information about the radiofrequency field intensity and distribution, after obtaining the target radiofrequency field map with higher resolution, the flip angle of the radiofrequency pulse excitation can be determined according to the target radiofrequency field map, and this flip angle is used as the corrected flip angle of the water-fat in-phase echo signal.

[0097] In this embodiment, by adjusting the initial radiofrequency field map with the second resolution to the first resolution to obtain the target radiofrequency field map that matches the water-fat in-phase echo image sequence in terms of pixel accuracy, the flip angle can be corrected based on the target radiofrequency field map with pixel accuracy matching, effectively improving the accuracy of the proton density map and longitudinal relaxation time map determined subsequently according to each flip angle.

[0098] In an exemplary embodiment, in step S202, adjusting the initial radiofrequency field map with the second resolution to the first resolution to obtain the target radiofrequency field map may include the following steps: performing linear interpolation on the initial radiofrequency field map with the second resolution to obtain the initial radiofrequency field map with the first resolution.

[0099] In practical applications, the initial RF field map with the second resolution can be obtained by performing multilinear interpolation on the initial RF field map, so as to obtain an initial RF field map with the same resolution as the water-fat in-phase echo image sequence, effectively improving the adjustment speed of the resolution.

[0100] In an exemplary embodiment, the echo sequence further includes a plurality of water-fat opposed-phase echo signals, where the water-fat opposed-phase echo signals are signals acquired when the hydrogen protons of water and fat in the lumbar spine are in different phases. For example, they can be acquired when the phases of the hydrogen protons of water and fat differ by x (x>0) degrees. Correspondingly, in step S103, using the initial transverse relaxation rate map and the initial field map as the initialization reconstruction parameters for water-fat separation to reconstruct the water-fat separation image of the lumbar spine may include the following steps:

[0101] The initial transverse relaxation rate map and the initial field map serve as the initialization reconstruction parameters for water-fat separation; based on the initialization reconstruction parameters, the water-fat opposed-phase echo signals, and the water-fat in-phase echo signals, perform water-fat separation image reconstruction; obtain the water image and the fat image of the lumbar spine according to the reconstruction result, and determine the tissue fraction map of the lumbar spine according to the water image and the fat image of the lumbar spine.

[0102] Specifically, due to the different chemical environments of the hydrogen protons in water and fat, there are differences in their precession frequencies, which is called chemical shift. When the magnetic field strength is constant, the precession frequency of the hydrogen protons in fat is slightly slower than that of the hydrogen protons in water. During magnetic resonance imaging, this frequency difference causes the signals of water and fat to change in phase over time. At certain specific time points, the signals of water and fat are in the same phase, and at this time, in the acquired echo signals, the signals of water and fat are superimposed on each other; while at other time points, the signals of water and fat are in different phases (for example, opposite), and at this time, in the acquired echo signals, the signals of water and fat cancel each other out. By collecting and processing these signals with different phases, water-fat separation can be achieved.

[0103] After obtaining the initial transverse relaxation rate map and the initial field map, the initial transverse relaxation rate map and the initial field map can be used as the initialization reconstruction parameters for water-fat separation, and combined with the water-fat opposed-phase echo signals and the water-fat in-phase echo signals, perform water-fat separation image reconstruction. In some exemplary embodiments, water-fat separation image reconstruction can be performed based on the dual-echo opposed-phase imaging technique.

[0104] Among them, dual-echo opposed-phase imaging uses a gradient echo sequence. After each radiofrequency pulse excitation, two echo signals are collected at the in-phase and opposed-phase time points of water and fat respectively, obtaining the in-phase echo of water and fat and the opposed-phase echo of water and fat. In the in-phase echo of water and fat, the signals of water and fat are added; in the opposed-phase echo of water and fat, the signals of water and fat are subtracted. By performing mathematical operations on these two echo signals, such as adding and subtracting the signal intensities of the in-phase image and the opposed-phase image, images of water and fat can be obtained respectively, realizing water-fat separation.

[0105] In the process of reconstructing the water-fat separation image, the initial reconstruction parameters can be used as the initial conditions, and combined with relevant iterative algorithms to continuously iterate and update the water image (Water map) and fat image (Fat map). When the iteration end condition is met, the water image and fat image containing the lumbar spine can be obtained. Then, according to the water image and fat image of the lumbar spine, the tissue fraction map of the lumbar spine can be determined, and then it can be used as the water-fat separation result.

[0106] In some exemplary embodiments, the water image and fat image can be directly used as the water-fat separation result of the lumbar spine; in other embodiments, the tissue fraction map, such as the Proton Density Fat Fraction (PDFF) map, can also be generated according to the water image and fat image in the reconstruction result. The water-fat separation result is obtained according to the water image, fat image and proton density fat fraction map. Among them, the proton density fat fraction map is an image that can reflect the relative proportion of fat content in the tissue structure. It presents the percentage of fat in the total proton density in the tissue in the form of an image by analyzing and calculating the components of fat and water in the magnetic resonance signal.

[0107] In this embodiment, by using the initial transverse relaxation rate map and the initial field map as the initial reconstruction parameters for water-fat separation, and then combining the water-fat opposed-phase echo signal to iteratively reconstruct the water image and fat image of the lumbar spine, it is possible to achieve accurate initialization of water-fat separation iterative reconstruction based on accurate and reliable initial parameter estimation results, effectively avoid falling into local extrema during the water-fat separation process, and avoid obtaining local optimal solutions, providing a necessary guarantee for accurately realizing multi-parameter quantification.

[0108] In an exemplary embodiment, after the step of reconstructing the water-fat separation image according to the initial reconstruction parameters, the water-fat opposed-phase echo signal and the water-fat in-phase echo signal, the following steps may further be included:

[0109] Obtain the target field map according to the reconstruction result; the target field map is obtained by iteratively updating the initial field map during the water-fat separation image reconstruction process; according to the target field map, obtain the quantitative susceptibility map corresponding to the lumbar spine.

[0110] In a specific implementation, during the process of reconstructing water-fat separated images, in addition to continuously iteratively updating the water image and the fat image, the initial field map and the initial transverse relaxation rate map R2* can also be iteratively updated. When the iteration end condition is met and the reconstruction result is obtained, the updated target field map can be acquired. Compared with the initial field map, by carefully iteratively updating in combination with the water-fat opposed-phase echo signal and the water-fat in-phase echo signal during the water-fat separation process, the accuracy of the target field map can be effectively improved.

[0111] Subsequently, according to the target field map, a quantitative susceptibility map (Quantitative Susceptibility Mapping, QSM) corresponding to the lumbar spine can be obtained. For example, after the target field map undergoes background removal, dipole deconvolution, and other processes, the quantitative susceptibility map can finally be obtained.

[0112] In this embodiment, by acquiring the target field map obtained during the process of reconstructing water-fat separated images and generating a quantitative susceptibility map according to the target field map, the accuracy of the multi-parameter quantitative imaging result of the lumbar spine can be further improved.

[0113] To enable those skilled in the art to better understand the above steps, the following provides an exemplary illustration of the embodiments of the present application through an example, but it should be understood that the embodiments of the present application are not limited thereto.

[0114] As Figure 3 shown, first, sequence design can be performed to obtain multi-flip angle multi-echo gradient echo images. During the sequence design process, multi-flip angle design and in-phase echo design are involved. Taking Figure 4 as an example, water-fat in-phase echo signals at two flip angles (i.e., α1 and α2) can be collected, including the water-fat in-phase echo signal at the α1 flip angle (which can be represented by ●) and the water-fat in-phase echo signal at the α2 flip angle (which can be represented by ▲). Among them, for the water-fat in-phase echo signals at the α1 and α2 flip angles, the hydrogen protons of water and fat can be determined to be in the same phase and collected when the echo time is 2.3 ms, 4.6 ms, and 6.9 ms. In addition, the water-fat opposed-phase echo signal at the α2 flip angle (which can be represented by ■) can also be obtained, and it can be determined that the hydrogen protons of water and fat are in different phases (such as opposite phases) and collected when the echo time is 3.1 ms, 5.4 ms, and 7.7 ms. The above-mentioned water-fat in-phase echo signals and water-fat opposed-phase echo signals are all presented in the form of echo images.

[0115] Thus, multi-flip angle multi-echo gradient echo images can be obtained. Among them, the images in the multi-flip angle multi-echo gradient echo images can be high-resolution images. For example, the resolution of the multi-flip angle multi-echo gradient echo images can be higher than a preset threshold. Subsequently, field map estimation, water-fat separation, and quantitative calculation of PD maps and T1 maps can be performed in combination with the multi-flip angle multi-echo gradient echo images to obtain accurate and stable multiple quantitative parameters.

[0116] Specifically, in field map estimation, the initialized map ( Figure 4 "R2* map without PDFF correction" in ) and can be determined according to the water-fat in-phase echo signals at at least one flip angle and a simplified signal model. In some embodiments, the initialized and can be determined according to the water-fat in-phase echo signal at one flip angle and a simplified signal model. At this time, the image signal-to-noise ratios of the water-fat in-phase echo signals corresponding to each of the multiple flip angles can be compared, and the water-fat in-phase echo signal with a higher signal-to-noise ratio can be selected to obtain the initial parameter estimation result, reducing the difficulty of water-fat separation. For example, if α1 and α2 are 3 degrees and 15 degrees respectively, the image obtained at α2 has a higher signal-to-noise ratio than the image obtained at α1. At this time, the initialized and can be determined using the water-fat in-phase echo signal obtained at α2. In other embodiments, the initialized and can be determined by combining the water-fat in-phase echo signals at multiple flip angles and a simplified signal model at the same time. For example, for the water-fat in-phase echo signal at each flip angle, the corresponding initialized and can be determined according to this sequence and the signal model; then, according to the and corresponding to each of the multiple flip angles, the final initial parameter estimation result is determined.

[0117] Subsequently, the B1 image of the radiofrequency field (i.e., the B Figure 4 map in 1t ) can be obtained, the resolution of the B1 image can be adjusted to an image with the same resolution as the multi-flip angle multi-echo gradient echo image through multi-linear interpolation, and the PD image and T1 image can be calculated according to the B1 image, the in the initial parameter estimation result, and the water-fat in-phase echo signal at the α1 flip angle and the water-fat in-phase echo signal at the α2 flip angle (i.e., the multi-flip angle echo sequence in the sequence design).

[0118] On the other hand, when performing water-fat separation, the initial parameter estimation result and , combined with the water-fat opposed-phase echo signal and the water-fat in-phase echo signal at the α2 flip angle (i.e., the multi-echo gradient echo image in the sequence design), are used for water-fat separation image reconstruction, and the final water image ( Figure 4 "Water map" in Figure 4 ), fat image ( "Fat map" in Figure 4 ), ( Figure 4 "R2* map" in ) and the target field map ( Figure 4 "Total field" in ) are obtained through iterative reconstruction. For the target field map , after background removal and dipole deconvolution processing, QSM can be finally obtained.

[0119] It should be understood that although the steps in the flowcharts involved in the above-described embodiments are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless there is a clear indication in this article, the execution of these steps has no strict order limit, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-described embodiments may include multiple steps or multiple stages. These steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily sequential, but can be executed alternately or in turn with at least a part of other steps or steps or stages in other steps.

[0120] Based on the same inventive concept, the embodiments of the present application also provide a magnetic resonance imaging device for the lumbar spine for implementing the above-mentioned magnetic resonance imaging method for the lumbar spine. The solution provided by this device for solving problems is similar to the solution described in the above method. Therefore, the specific limitations in one or more embodiments of the magnetic resonance imaging device for the lumbar spine provided below can refer to the limitations for the magnetic resonance imaging method for the lumbar spine in the above text, and will not be repeated here.

[0121] In an exemplary embodiment, as Figure 5 shown, a magnetic resonance imaging device for the lumbar spine is provided, including:

[0122] A sequence acquisition module 501, configured to acquire an echo sequence for the lumbar spine during magnetic resonance imaging; the echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signal is a signal acquired when the hydrogen protons of water and fat are in the same phase;

[0123] An initial parameter estimation module 502 is configured to determine an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the inhomogeneity of the static magnetic field applied to the lumbar spine according to the signal intensities of the water-fat in-phase echo signals, the echo times of the water-fat in-phase echo signals, and a pre-constructed signal model; in the signal model, the signal intensity of the water-fat in-phase echo signal is a signal jointly determined by the transverse relaxation rate map at the in-phase moment of the hydrogen protons of water and fat and the inhomogeneous magnetic field map of the static magnetic field.

[0124] A water-fat separation module 503 is configured to use the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation to reconstruct a water-fat separation image of the lumbar spine.

[0125] In one embodiment, the water-fat in-phase echo signals include a plurality of water-fat in-phase echo signals obtained by exciting with multiple radio frequency pulses, and the plurality of water-fat in-phase echo signals correspond to different flip angles.

[0126] The apparatus further includes:

[0127] A first quantitative parameter calculation module is configured to obtain a proton density map and a longitudinal relaxation time map of the lumbar spine according to the initial transverse relaxation rate map, the flip angles corresponding to the plurality of water-fat in-phase echo signals, and the repetition time between the multiple radio frequency pulse excitations.

[0128] In one embodiment, the water-fat in-phase echo signal corresponds to a water-fat in-phase echo image with a first resolution.

[0129] The first quantitative parameter calculation module is further configured to:

[0130] Obtain an initial radio frequency field map corresponding to the radio frequency pulse excitation; the second resolution corresponding to the initial radio frequency field map is less than the first resolution.

[0131] Adjust the initial radio frequency field map with the second resolution to the first resolution to obtain a target radio frequency field map.

[0132] Determine the flip angle of the radio frequency pulse excitation according to the target radio frequency field map as the flip angle corresponding to the water-fat in-phase echo signal.

[0133] In one embodiment, the first quantitative parameter calculation module is further configured to:

[0134] Perform linear interpolation on the initial radio frequency field map with the second resolution to obtain the initial radio frequency field map with the first resolution.

[0135] In one embodiment, the echo sequence further includes a plurality of water-fat opposed-phase echo signals, which are signals acquired when the hydrogen protons of water and fat in the lumbar spine are in different phases;

[0136] The water-fat separation module 503 is configured to:

[0137] Use the initial transverse relaxation rate map and the initial field map as the initialization reconstruction parameters for water-fat separation;

[0138] Perform water-fat separation image reconstruction according to the initialization reconstruction parameters, the water-fat opposed-phase echo signals, and the water-fat in-phase echo signals;

[0139] Obtain the water image and the fat image of the lumbar spine according to the reconstruction result, and determine the tissue fraction map of the lumbar spine according to the water image and the fat image of the lumbar spine.

[0140] In one embodiment, the apparatus further includes a second quantitative parameter calculation module, which is configured to:

[0141] Obtain a target field map according to the reconstruction result; the target field map is obtained by iteratively updating the initial field map during the water-fat separation image reconstruction;

[0142] Obtain the quantitative susceptibility map corresponding to the lumbar spine according to the target field map.

[0143] Each module in the above magnetic resonance imaging apparatus for the lumbar spine can be implemented in whole or in part by software, hardware, and their combination. The above modules can be embedded in the processor of the computer device in hardware form or independent of it, or stored in the memory of the computer device in software form, so that the processor can call and execute the operations corresponding to the above modules.

[0144] In an exemplary embodiment, a computer device is provided. The computer device can be a server, and its internal structure diagram can be as Figure 6As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, abbreviated as I / O), and a communication interface. Among them, the processor, the memory, and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store magnetic resonance imaging data including lumbar echo sequences. The input / output interface of the computer device is used to exchange information between the processor and external devices. The communication interface of the computer device is used to communicate with external terminals through a network connection. When the computer program is executed by the processor, it implements a magnetic resonance imaging method for the lumbar spine.

[0145] In an exemplary embodiment, a computer device is provided. The computer device may be a terminal, and its internal structure diagram may be as Figure 7 shown. The computer device includes a processor, a memory, an input / output interface, a communication interface, a display unit, and an input device. Among them, the processor, the memory, and the input / output interface are connected through a system bus, and the communication interface, the display unit, and the input device are connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The input / output interface of the computer device is used to exchange information between the processor and external devices. The communication interface of the computer device is used to communicate with external terminals in a wired or wireless manner. The wireless manner can be achieved through WIFI, a mobile cellular network, near field communication (Near Field Communication, NFC), or other technologies. When the computer program is executed by the processor, it implements a magnetic resonance imaging method for the lumbar spine. The display unit of the computer device is used to form a visually visible picture, which can be a display screen, a projection device, or a virtual reality imaging device. The display screen can be a liquid crystal display screen or an electronic ink display screen. The input device of the computer device can be a touch layer covering the display screen, or a button, a trackball, or a touchpad provided on the computer device housing, or an external keyboard, touchpad, or mouse, etc.

[0146] Those skilled in the art can understand that Figure 6 and Figure 7The structure shown is only a block diagram of some structures related to the solution of this application, and does not constitute a limitation on the computer device to which the solution of this application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine some components, or have different component arrangements.

[0147] In one embodiment, a computer device is provided, including a memory and a processor. A computer program is stored in the memory, and when the processor executes the computer program, the steps in the above method embodiments are implemented.

[0148] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0149] In one embodiment, a computer program product is provided, including a computer program. When the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0150] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use, and processing of relevant data need to comply with relevant regulations.

[0151] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The databases involved in the embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the embodiments provided in the present application can be general-purpose processors, central processors, graphics processors, digital signal processors, programmable logic devices, data processing logics based on quantum computing, artificial intelligence (AI) processors, etc., without limitation.

[0152] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope recorded in the present application.

[0153] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. A magnetic resonance imaging method for the lumbar spine, characterized in that, The method includes: Obtaining an echo sequence for the lumbar spine during magnetic resonance imaging; the echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signals are signals acquired when the hydrogen protons of water and fat are in the same phase; Determining an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the inhomogeneity of the static magnetic field applied to the lumbar spine according to the signal intensities of the water-fat in-phase echo signals, the echo times of the water-fat in-phase echo signals, and a pre-constructed signal model; in the signal model, the signal intensity of the water-fat in-phase echo signal is a signal jointly determined by the transverse relaxation rate map at the moment when the hydrogen protons of water and fat are in the same phase and the inhomogeneous magnetic field map of the static magnetic field; Using the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation to reconstruct a water-fat separation image of the lumbar spine.

2. The method according to claim 1, wherein The water-fat in-phase echo signals include multiple water-fat in-phase echo signals obtained by multiple radio frequency pulse excitations, and the multiple water-fat in-phase echo signals correspond to different flip angles; The method further includes: Obtaining a proton density map and a longitudinal relaxation time map of the lumbar spine according to the initial transverse relaxation rate map, the flip angles corresponding to the multiple water-fat in-phase echo signals, and the repetition time between the multiple radio frequency pulse excitations.

3. The method according to claim 2, wherein The water-fat in-phase echo signals correspond to water-fat in-phase echo images with a first resolution; The flip angle corresponding to the water-fat in-phase echo signal is determined through the following steps: Obtaining an initial radio frequency field map corresponding to the radio frequency pulse excitation; the second resolution corresponding to the initial radio frequency field map is less than the first resolution; Adjusting the initial radio frequency field map with the second resolution to the first resolution to obtain a target radio frequency field map; Determining the flip angle of the radio frequency pulse excitation according to the target radio frequency field map as the flip angle corresponding to the water-fat in-phase echo signal.

4. The method according to claim 3, characterized in that, Adjusting the initial radio frequency field map with the second resolution to the first resolution includes: Performing linear interpolation on the initial radio frequency field map with the second resolution to obtain the initial radio frequency field map with the first resolution.

5. The method according to any one of claims 1 to 4, characterized in that The echo sequence further includes multiple water-fat out-of-phase echo signals, and the water-fat out-of-phase echo signals are signals acquired when the hydrogen protons of water and fat in the lumbar spine are in different phases; The step of using the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation to reconstruct a water-fat separation image of the lumbar spine includes: Using the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation; Performing water-fat separation image reconstruction according to the initialization reconstruction parameters, the water-fat out-of-phase echo signals, and the water-fat in-phase echo signals; Obtaining a water image and a fat image of the lumbar spine according to the reconstruction result, and determining a tissue fraction map of the lumbar spine according to the water image and the fat image of the lumbar spine.

6. The method according to claim 5, characterized in that, After the step of performing water-fat separation image reconstruction according to the initialization reconstruction parameters, the water-fat out-of-phase echo signals, and the water-fat in-phase echo signals, it further includes: Obtain a target field map according to the reconstruction result; the target field map is obtained by iteratively updating the initial field map during the reconstruction process of the water-fat separation image; Obtain a quantitative susceptibility map corresponding to the lumbar spine according to the target field map.

7. A magnetic resonance imaging device for the lumbar spine, characterized in that, The device includes: A sequence acquisition module, configured to acquire an echo sequence for the lumbar spine during magnetic resonance imaging; the echo sequence includes water-fat in-phase echo signals corresponding to different echo times, and the water-fat in-phase echo signals are signals acquired when the hydrogen protons of water and fat are in the same phase; An initial parameter estimation module, configured to determine an initial transverse relaxation rate map corresponding to the lumbar spine and an initial field map characterizing the static magnetic field inhomogeneity applied to the lumbar spine according to the signal intensities of the water-fat in-phase echo signals, the echo times of the water-fat in-phase echo signals, and a pre-constructed signal model; the signal intensity of the water-fat in-phase echo signal in the signal model is a signal jointly determined by the transverse relaxation rate map at the moment when the hydrogen protons of water and fat are in the same phase and the static magnetic field inhomogeneity field map; A water-fat separation module, configured to use the initial transverse relaxation rate map and the initial field map as initialization reconstruction parameters for water-fat separation, and reconstruct the water-fat separation image of the lumbar spine.

8. A computer device, comprising a memory and a processor, the memory storing a computer program, characterized in that, When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

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